Sealant Layer Requirements in Coextruded Blown Film on High-Speed VFFS Lines

In coextruded blown film structures for vertical form-fill-seal (VFFS) equipment, the sealant layer is typically a blend of ATTANE 4301 (density 0.904 g/cm³ per ASTM D792, melt index 0.9 g/10 min at 190°C/2.16 kg per ASTM D1238, melting peak approximately 121°C per ASTM D3418) with a linear low-density polyethylene (LLDPE) or low-density polyethylene (LDPE) carrier to balance hot tack strength against bubble stability on high-output lines. Industrial blown film trials on 3-layer coex lines with die diameter 400 mm, die gap 2.0 mm, blow-up ratio 2.5:1, and frost line height 8–12 times die diameter have shown that 30–70 wt% of the VLDPE in the sealant layer permits heat seal initiation temperature reductions of 5–15°C relative to conventional octene-LLDPE sealant grades, as measured by heat seal initiation per ASTM F2029 on films conditioned at 23°C and 50% RH. The extruder screw is configured as a barrier design with Maddock mixing section and L/D 30:1, and the melt temperature profile is maintained between 220°C and 250°C; sustained operation above 280°C produces measurable gel counts from oxidative degradation within 30 minutes of residence time, which manifests as visible specks in the sealant layer and intermittent seal failures on VFFS lines running above 80 pouches/min. Additive packages typically include erucamide slip at 300–800 ppm and silica antiblock at 1,000–2,000 ppm, but formulations destined for high-clarity lidding should omit antiblock because it raises haze above 15% at 50 µm film thickness. Compliance for direct food contact requires FDA 21 CFR 177.1520(c) under conditions of use B through H, and union lists under EU Regulation (EU) No 10/2011 with an overall migration limit of 10 mg/dm². Terminal products include frozen vegetable bags, dried fruit and nut pouches, stand-up pouch sealant webs, and lidding films for thermoformed trays, where the sealant layer thickness ranges from 10 µm to 30 µm within structures of 50–120 µm total thickness; sealant layer formulation must account for the specific hot tack requirement of the converter, with higher VLDPE content favouring lower seal initiation but reducing melt strength at the die.

Cast film extrusion of pallet unitization stretch wrap employs an LLDPE-rich formulation modified with 20–40 wt% ATTANE 4301 to raise Elmendorf tear resistance and reduce machine-direction tear propagation on hand-applied and pre-stretched films. A typical cast film line comprises a 150 mm single-screw extruder with L/D 30:1, a flat die of 0.6–1.0 mm gap, and a chill roll maintained at 15–25°C with an air knife positioned to suppress edge pinning defects; line speeds routinely reach 250–450 m/min, and the VLDPE fraction necessitates higher winding tension control due to its lower modulus and higher surface cling relative to standard octene-LLDPE. The material addition level is confined to the range where cast film curl and blocking are not elevated above production tolerance; trials have identified that exceeding 40 wt% VLDPE increases cling force to levels that cause intermittent roll telescoping unless slip additives are added at the expense of cling performance. Cling force is tested per ASTM D4649-20 for stretch wrap materials, and machine direction stretch retention is evaluated per ASTM D5459; the combination of 20–40 wt% VLDPE with an ethyl vinyl acetate (EVA) cling layer is typically avoided because the two components compete for surface migration and produce irregular cling distribution. The extrusion melt temperature is kept at 230–260°C; above 260°C, surface oxidation can create pinholes in films below 17 µm. Terminal products include pre-stretched hand wrap, machine film for rotary ring wrappers, and heavy-gauge (20–35 µm) agricultural bale wrap where puncture resistance during high-speed application is the controlling specification.

What Constrains Melt Curtain Stability When ULDPE Is Extrusion-Coated Onto Paperboard?

Extrusion coating of paperboard for aseptic beverage cartons and single-serve sachets imposes a narrow processing window defined by melt curtain stability and adhesion to corona-treated board. When 10–30 wt% ATTANE 4301 is blended into LDPE (melt index 4–8 g/10 min per ISO 1133-1:2022), the lower melt elasticity reduces neck-in by 10–20% at constant melt temperature and air gap, but the curtain becomes more sensitive to draw resonance below 10 wt% VLDPE; above 30 wt%, output rate must be reduced because melt tension at the die lip falls below the threshold needed for stable edge bead formation. Coating lines with a 4.5-inch extruder, L/D 30:1, barrier screw, and flat die of 0.5 mm gap operate at melt temperature 310–330°C, air gap 150–250 mm, and line speed 150–300 m/min; the high melt temperature is necessary for adhesion to paperboard but shortens the induction time for oxidative gel formation, so the extruder barrel is purged with nitrogen at the feed throat at 2–5 L/min. Adhesion to paperboard requires corona treatment of substrate to surface energy above 38 dyn/cm immediately before coating; failure to maintain this level results in interfacial delamination during downstream scoring and folding. Compliance for food contact is governed by FDA 21 CFR 176.170(c) for components of paper and paperboard in contact with aqueous and fatty foods, and EU Regulation (EU) No 10/2011 for plastic layers in contact with food, with overall migration testing per EN 1186-1; sachets for aqueous liquids additionally require seal strength after sterilization at 121°C for 30 minutes. Terminal products include aseptic brick carton inners, paper-based sachet webs, and cupstock for dairy closures, where coating weights range from 15 g/m² to 35 g/m².

Biaxially oriented blown film for bottle collation shrink sleeves and tamper-evident closures incorporates 15–35 wt% ATTANE 4301 into an LLDPE/LDPE base to lower orientation stress and improve free shrink uniformity at lower shrink tunnel temperatures. In the double-bubble process, the primary tube is extruded at melt temperature 190–210°C, quenched, and reheated to 110–125°C for transverse and machine direction orientation before air expansion at BUR 3.5–4.5; the VLDPE fraction reduces the incidence of bubble breaks during the second inflation stage by decreasing crystalline memory, but output on lines without infrared reheating is limited by the time required for uniform heat transfer through the collapsed tube. Free shrink and shrink tension are evaluated per ASTM D2732 and ASTM D2838, respectively, with compliance for direct food contact subject to FDA 21 CFR 177.1520(c); when the film is used as a tamper-evident sleeve for pharmaceutical packaging, extractables testing is performed according to USP 661.1 for plastic packaging materials. Additive packages are restricted to non-migrating slip agents because conventional migratory slip reduces the coefficient of friction to the point where shrink sleeves slip during automatic application. Terminal products include bottle collation shrink film for beverage multipacks, tamper-evident shrink sleeves for bottled pharmaceuticals, and box overwrap for frozen seafood, with typical film thickness of 35–75 µm.

Heavy-Duty Sack Film Puncture Resistance and Drop-Test Compliance

Heavy-duty shipping sacks and FIBC liners produced from 100 wt% ATTANE 4301 or blends containing up to 20 wt% LDPE are extruded on blown film lines with die diameter 500 mm, die gap 2.5–3.0 mm, BUR 2.5:1, and melt temperature 190–220°C. The low density and narrow molecular weight distribution contribute to a dart impact resistance (per ASTM D1709, Method A) that at 80 µm gauge typically falls in the range of 300–600 g for pure VLDPE film conditioned at 23°C and 50% RH; however, published data for this specific configuration is limited, and batch-to-batch variability on single-layer lines without internal bubble cooling can reduce this value by 10–15%. Compliance for dangerous goods packaging references UN 13H2 performance tests under ADR/RID 6.1 for flexible plastics sacks, and mechanical properties are verified per ISO 527-3 and ISO 6383-1; for petrochemical powders, the liner must also meet static decay criteria of MIL-PRF-81705D at 12% RH. Terminal products include FIBC inner liners, petrochemical powder sacks, fertilizer bags, and grain sacks at gauge 50–120 µm.

When Sterile Barrier Packaging Requires Sub-Ambient Flexibility Without Plasticiser Migration

Medical device overwrap and sterile barrier pouches formulated from ATTANE 4301 at 100 wt% or in blends with up to 30 wt% EVA rely on the low glass transition and absence of phthalate plasticisers to maintain seal integrity at temperatures as low as -40°C. Blown film production for cleanroom-adapted lines uses polished contact surfaces and HEPA-filtered air cooling, with die gap 1.8–2.2 mm, melt temperature 210–240°C, and output below 150 kg/h to control gel contamination; the extruder is dedicated to medical-grade polyethylene because purge transition from commodity films leaves unacceptable levels of contamination for subsequent seal-strength testing. Compliance includes ISO 11607-1 for terminally sterilized medical device packaging, USP Class VI biological reactivity testing, and ASTM F88 for seal strength; extractables profiling follows ISO 10993-12, and the film must demonstrate compatibility with ethylene oxide sterilization cycles at 55°C and gamma irradiation doses up to 50 kGy per ISO 11135 and ISO 11137. Terminal products include sterile barrier pouches, lidding for rigid medical trays, and bulk nonwoven overwrap for surgical kits, with film thickness 40–80 µm.